1. Field of the Invention
The present invention relates to a device which interrupts the flow of hydraulic fluid to a failure point in the circuit of a park brake or service brake system. More particularly, the present invention provides a fluid flow shut-off device which stops the flow of hydraulic oil to the brake calipers on any "off-highway" truck in the event of a circuit failure.
2. Prior Art
Safety valves or shut-off devices which are used for hydraulic and/or pneumatic braking circuits are well known in the prior art. The main purpose of most of these devices is to interrupt the flow of oil or air to the failed portion of the braking circuit thus allowing the remaining portions of the brake circuit to remain fully operational without an appreciable loss of power.
A prior art patent, U.S. Pat. No. 4,212,498 to Kawaguchi, discloses a control valve for controlling the hydraulic pressure in the rear brake cylinders. The device includes a proportioning valve with a valve piston for opening and closing a fluid passage to the rear wheel cylinder. The Kawaguchi device maintains proper distribution of braking power to the front and rear wheels even when a pressure failure occurs.
In U.S. Pat. No. 4,159,755 to Kang et al, a control cylinder is disclosed which has an inlet portion connected to the hydraulic pressure source and first and second outlets connected to the front and rear wheels, respectively. The Kang patent provides for separate systems for the front and the rear wheels so that the loss of brake pressure in a hydraulic line to one set of wheels does not affect the hydraulic pressure or the braking effect at the other wheels. Another prior art device, disclosed in U.S. Pat. No. 3,753,601 to Hensley, is positioned intermediately between the master cylinder and the brake assembly. Upon the occurence of any leak, a valve in the Hensley device moves from a first position to a second position to prevent further discharge of fluid to the defective brake assembly.
In U.S. Pat. No. 4,236,759 to Lysenko, a safety valve is disclosed which functions to protect against substantial losses of hydraulic fluid from a braking system due to failure, and which is applicable for use on large off-highway vehicles. The safety valve includes a cylindrically shaped chamber with an opening at both ends, which responds to fluid volume transfer through the chamber. A ball moves axially in the chamber in direct response to the volumetric flow and will obstruct an outlet opening thus inhibiting further fluid volumes from exiting the chamber. The Lysenko device is used primarily to prevent loss of hydraulic fluid from a common reservoir, thus circumventing the loss of the vehicle's braking capacity.
No prior art device is disclosed which can limit the flow or loss of hydraulic fluid to a measurably small amount. No prior art device disclosed can be readily used on both the park brake and service brake systems of a large "off-highway" vehicle. The prior art does not disclose a device which operates by transferring an input pressure signal to a similar output pressure signal without transferring hydraulic fluid from the input to the output side of the device during its operation.